Hearing Voices – Underpinnings of Auditory Hallucinations

In “The Origin of Consciousness in the Breakdown of the Bicameral Mind,” Julian Jaynes suggested back in 1976 that schizophrenia — like spirit possession and imaginary playmates — was a vestige of our brain’s bicameral heritage. Jaynes believed that in man’s early history, the left and right hemispheres of the brain did not “talk” to each other. They failed to communicate effectively across the corpus callosum, the bridge from one hemisphere to another. The result was, to Jaynes, obvious: People used to hear voices. Nowadays, most people who hear voices inside their head are diagnosed as schizophrenics.

What exactly is going on in the brain during auditory hallucinations? And is the act of hearing voices inside one’s head always incontrovertible evidence of psychosis? In recent years, the use of MRIs, PET scans and other imaging technologies has given researchers some specific clues about these and other questions.

Auditory hallucinations are considered by many medical professionals to be the most frequent and reliable symptom of psychosis. More than 70 percent of diagnosed schizophrenics suffer from them at some point in the course of their disease. In Frontiers in Neuroscience, Kenneth Hugdahl and a group of researchers at the University of Bergen, Norway, published a recent study of temporal disturbances during auditory hallucinations. The main question the scientists sought to answer was whether there are identifiable brain tissue abnormalities in schizophrenic patients who frequently hear voices. And there are. Confirming earlier studies, Hugdahl’s group found significantly reduced grey matter density in the left peri-Sylvian region, an area of the cerebral cortex that includes Broca’s Area, Wernicke’s Area, and other language-processing structures. Lesions to the so-called peri-Sylvian region of the left superior temporal gyrus can cause loss of language capabilities. The researchers found that “hallucinating patients had significantly reduced grey matter density in the left superior temporal gyrus, the medial prefrontal cortex in peri-ventricular areas, and in the thalamus.”

In addition to identifying a pathology in the speech processing areas of the left temporal lobe of schizophrenics, the researchers suggested a specific mechanism for the abnormalities: low concentrations of glutamate. “We suggest that glutamatergic transmission may be deficient in auditory hallucinations which may trigger the experience of hearing voices,” the group at the University of Bergen concluded. Antipsychotic drugs like risperidone typically target dopamine receptors. Stimulating glutamate receptors as a treatment is still unproven. However, drug maker Lilly has been working on one such drug, known only as LY2140023, for several years.

Meanwhile, earlier work from Great Britain published in the American Journal of Psychiatry has also implicated a region in the right brain, specifically the right middle temporal gyrus, which responds to external speech. Normal people respond to external speech with greater left side activity. In schizophrenics, this region in the right brain is hyperactive, suggesting a possible compensatory increase due to left-hemisphere language processing dysfunctions. The Norwegian researchers suggested that “auditory hallucinations ‘compete’ with external speech for processing sites within the temporal cortex. This notion of competition is consistent with the use of listening to music or speech as a means of alleviating auditory hallucinations.” Such “attentional strategies” help many schizophrenics modulate the voices, and they also suggest ways of assessing specific therapeutic interventions for auditory hallucinations.

Most notably, the group of British researchers hypothesized that if such language dysfunction “has its origins in early brain development, it might be possible to detect abnormally lateralized auditory processes in children who will later develop schizophrenia.”

The past few years have also seen the development of a radical counter-movement that seeks to normalize the act of hearing voices. The movement is said to have originated in the Netherlands and the U.K. Intervoice, which bills itself as “the international community for hearing voices,” says they have found that many people who hear voices “are not troubled by them or have found their own ways of coping with them outside of psychiatric care.” Those voice hearers who are “overwhelmed by the negative and disempowering aspects of the experience” are often diagnosed as schizophrenics — “a harmful and stigmatizing concept,” in the opinion of Intervoice.

References

AGUILAR, E., SANJUAN, J., GARCIAMARTI, G., LULL, J., & ROBLES, M. (2008). MR and genetics in schizophrenia: Focus on auditory hallucinations European Journal of Radiology, 67 (3), 434-439 DOI: 10.1016/j.ejrad.2008.02.046

Woodruff, P., Wright, I., Bullmore, E., Brammer, M., Howard, R., et. al. (1997). Auditory Hallucinations and the Temporal Cortical Response to Speech in Schizophrenia: A Functional Magnetic Resonance Imaging Study. American Journal of  Psychiatry, 154, 1676-1682.

Barta, P., Pearlson, G., Powers, R., Richards, S., and Tune, L. (1990). Auditory hallucinations and smaller superior temporal gyral volume in schizophrenia. American Journal of Psychiatry, 147, 1457-1462.

Hugdahl, K., Loberg, E., Specht, K., Steen, V, Wageningen, H., and Jorgensen, H. (2008). Auditory hallucinations in schizophrenia: the role of cognitive, brain structural and genetic disturbances in the left temporal lobe. Frontiers in Human Neuroscience, 1, Article 6.